The present invention relates to a power-shift transmission having an electronic controller for controlling the selection of gear engagements to produce a speed ratio between the input and output of the transmission. In particular, the present invention relates to the default gear selection used by the controller when the controller is energized upon start-up of the associated vehicle.
In the field of transmission systems for work vehicles, such as agricultural tractors and construction vehicles, various transmission configurations and control schemes have been proposed and are in use. Such transmissions typically include a collection of intermeshing gears either fixed to transmission shafts or rotating freely on the shafts. Clutches associated with the freely rotating gears may be selectively engaged to establish a series of speed ratios between an engine output shaft and a transmission output shaft to transmit engine torque at a desired speed to driven wheels of the vehicle. Control systems for commanding engagement of the clutches typically include an electronic controller which responds to operator controls, such as an upshift/downshift lever, a forward/neutral/reverse (FNR) lever and the like in the vehicle cab. The control system sends electric signals to hydraulic valves that channel pressurized fluid to the clutches. The control systems cause the clutches to engage and disengage in predetermined combinations of gears to generate different gear ratios in the associated transmission so that engine power is appropriately applied to the drive wheels.
The electronic systems for controlling transmissions of large, off-road work vehicles typically provide for various modes of operation and for control of a large number of forward and reverse gear ratios. The various operation modes and large number of gear ratios allow an operator to efficiently and accurately control the movement of these vehicles under a variety of differing load conditions without overloading the engine or clutches of the drivetrain, and without causing engine overspeed. The operator may use an upshift/downshift control lever to request a speed change via the selection of an appropriate gear ratio, wherein the selection occurs by control of solenoid valves which control engagement of hydraulic clutches corresponding to the appropriate gear ratio. In a certain system configured for operation in a forward manual mode, actuation of the control lever causes the system to upshift by a single gear ratio change to the next higher gear ratio.
One of the design considerations which must be addressed for transmissions of the type discussed above is the selection of default gear ratios upon system start-up. More specifically, when a vehicle is started, power is applied to the transmission controller and it is required to select a default forward gear and a default reverse gear. If these gears are not selected, the controller has no reference gear for purposes of selecting a gear when the FNR lever is moved from neutral to either forward or reverse immediately after start-up. Accordingly, the default forward and reverse start-up gears are typically stored in non-volatile memory of these systems and are typically not capable of being modified in a limited and controlled fashion. In particular, these types of transmission controls either do not allow a change in the default gears, or permit almost unlimited changing of the default gears such that they may be changed every time a different operator uses the vehicle.
One problem with not providing the ability to modify the default gears is that different vehicle uses may provide improved operator productivity if the default gears can be changed. However, the problem with not limiting the ability to change the start-up gears is an unexpected start-up gear selection by one operator when another operator has changed the start-up gears. Additionally, without limiting the ability to modify the start-up gears there may be an inadvertent change by the operator.
In view of the foregoing problems, it would be desirable to provide a limited ability to change start-up gears to better fit the overall and ongoing intended use of the vehicle associated with the transmission. To this end, it would be desirable to select the default gears from a user interface physically displaced from the operator cab or station of the vehicle but coupled to a databus in the vehicle which permits communication between vehicle controllers.
The present invention provides a control system for a transmission of the type used in a work vehicle including an engine and driven wheels. The transmission is coupled between the engine and the driven wheels to transmit power therebetween. The transmission includes a plurality of gears and associated clutches engageable in predetermined combinations by the control system to define transmission gear ratios within the transmission.
One embodiment of the control system includes an operator interface for generating a direction signal representative of the desired direction of the work vehicle and a memory circuit for storing a default start-up gear ratio value. A first control circuit is coupled to the operator interface and the memory circuit, and receives the direction signal and selectively engage the clutches in a combination corresponding to the default start-up gear ratio value when power is applied to the control circuit upon vehicle start-up. A databus is coupled to the first control circuit and includes a communication interface which is also coupled to a second control circuit. The second control circuit is configured to control a predetermined function of the vehicle. The system also includes a system interface separate from the vehicle and adapted to communicate with the communication interface to communicate with at least the memory circuit so that the default start-up gear ratio value can be transmitted from the system interface to the memory circuit for storage therein.
Another embodiment of the control system includes a lever coupled to a transducer which generates a direction signal representative of at least one of a forward direction and a reverse direction of the work vehicle, and a memory circuit for storing default start-up forward and reverse gear ratio values. A first control circuit is coupled to the transducer and the memory circuit, receives the direction signal, and selectively engages the clutches in a first combination corresponding to the default forward gear ratio value when electrical power is applied to the control circuit upon vehicle start-up and the direction signal is representative of a forward direction. The control circuit selectively engages the clutches in a second combination corresponding to the default reverse gear ratio value when electrical power is applied to the control circuit upon vehicle start-up and the direction signal is representative of a reverse direction. A databus is coupled to the first control circuit and includes a communication interface. A second control circuit is coupled to the databus and controls a predetermined function of the vehicle. A system interface, separate from the vehicle, communicates with at least the memory circuit such that the default start-up gear ratio value can be transmitted from the system interface to the memory circuit for storage therein.
Another embodiment of the control system includes means for generating a direction signal representative of the desired direction of the work vehicle and means for storing a default start-up gear ratio value. A first control means is provided for receiving the direction signal and selectively engaging the clutches in a combination corresponding to the gear ratio value when power is applied to the control circuit upon vehicle start-up, and a databus is coupled to the first control means and includes a communication interface. A second control means is coupled to the databus and controls a predetermined function of the vehicle. An interface means is provided for communicating with the communication interface to communicate with at least the means for storing so that the default start-up gear ratio value can be transmitted from the interface means to the means for storage.